Method and apparatus for manufacture of tubular bodies by electroslag remelting

ABSTRACT

The disclosure provides an apparatus and a method for producing tubular bodies by an electroslag melting process. Metallic electrodes are suspended vertically with their lower ends projecting into a mould. The lower ends of the metallic electrodes are melted and form a pool of molten metal, from which the desired tubular body is formed. As the lower ends of the metallic electrodes are consumed the mould is raised so that contact is maintained between the lower ends of the metallic electrodes and the pool of molten metal.

[11] 3,834,443 Sept. 10,1974

United States Patent [191 Ujiie 3,507,968 4/1970 Parsons......................... 3,610,319 10/1971 Kleinhagauer et al..... 3,683,997 8/1972 Uziie et 3,713,476 1/1973 [75] Inventor: Akira Ujiie, Kobe, Japan [73] Assignee: Mitsubishi Jukogyo Kabushiki Primary Examiner-J. Spencer Overholser Assistant Examiner-John E. Roethel Kalsha Tokyo Japan Attorney, Agent, 0r"Firm-Cushman, Darby & Jan. 9, 1973 Cushman 22] Filed:

[21] Appl. No.: 322,229

ABSTRACT d yedd nHhne hfi Tanm t -C S G m de m mm mm t 0 M d S no ehd Un .w 6 h S 0 ullpt wr m mmm w w um mm y llcfe a ak h SS a nee q ts d w A wwrk m a 6., Fma w .l e e v nmhm OM66 or r e o wk h mmun mm oo v. S.l d b ndo C .enp .BmShe r. m m m C m mn 4 222 M 5N5 2 mu 7 & 4 2 4 a 2 6 t n 5 1 a M n D m 6 m n 1 m u m r u .w mm r. u n. P m m n n "W" .m m m m t n "mm w W m H.- a J "u w. mrm A In n "u h m mm& W L n 4, s n F UMF 1 ll] 0 2 8 3 555 lrLrL tallic electrodes are consumed the mould is raised so m a m mm rm wk 0 hm ef m no 0 WP m t 0 d n a .ms me .mm n m 1 1e MC 3 n 06 m me .I S m E T A P. mm mm mT .ms D RE T I N U Q 5 3,421,569 l/l969 Neumann.......,...................... 164/86 8 Claims, 3 Drawing Figures [[lllllllllllllfVfli PAIENTEDSEPIOISM 1884.443

SHEET 1!]? 2 METHOD AND APPARATUS FOR MANUFACTURE OF TUBULAR BODIES BY ELECTROSLAG REMELTING FIELD OF THE INVENTION This invention relates to an apparatus and a method for producing tubular bodies such as metallic tubes by electroslag re-melting of metallic electrodes.

BACKGROUND OF THE INVENTION In Japan, in the production of tubular bodies by remelting metallic electrodes in a metal mould by an electroslag melting process, the metallic electrodes are arranged above a stationary metal mould and are fed continuously into the metal mould by feeding means. The metallic electrodes are melted continuously in the metal mould by electroslag melting to form a pool of molten metal which cools and solidifies continuously into the shape of a tubular body and is continuously drawn downwardly from the metal mould by drawing means, to obtain the product tubular body. Therefore, the height of the apparatus for forming a tubular body as described above must be at least equal to the total length of the tubular body to be produced plus the total length of the metallic electrodes. The total length of the metallic electrodes, in most cases, is substantially equal to the total length of the tubular body to be produced, so that the total height of the production apparatus is large and is substantially equal to twice the length of the tubular body product. In order to reduce the height of the production apparatus, a method may be employed in which each metallic electrode is cut into short pieces and these short pieces are fed into the metal mould one after another upon being connected with each other by welding. This method, however, calls for means for welding the electrode pieces, which renders the construction of the apparatus extremely complicated. In addition, the welding operation involves much difficulty particularly when the tubular body to be produced is large in size and thickness, because in this case the thickness of metallic electrodes required is also large. Thus, this method is impracticable. In the case where the tubular body to be produced is small in size and thickness, the height of the production apparatus may be reduced by using a metallic electrode in the form of a wire wound on a reel. However, the use of such metallic electrodes is economically unacceptable, because such metallic electrodes are very expensive and increase the production costs to a commercially unacceptable level.

It has been the practice heretofore to increase the height of the building or to construct a deep pit in the floor of the building which houses the apparatus. This not only involves considerable construction work but also necessitates a lifting jack of considerable height, for raising metallic electrodes, which in turn requires additional construction work for the lifting jack. Furthermore, the apparatus described above has the disadvantage that, since the metal mould is fixed, it must be provided with additional facilities, such as metallic. electrode feeding means and drawing means for drawing the product tube from the metal mould, which add to the cost. This disadvantage has been aggravated particularly when the product tube is large in size and thickness, because the feeding means and drawing means must be large in size.

SUMMARY OF THE INVENTION According to one aspect of the invention, there is provided a method of producing a tubular body which comprises continuously melting the lower ends of a plurality of metallic electrodes in an electroslag melting process to form a pool of molten metal in a mould in which the desired tubular body is formed from the molten metal and continuously raising the mould as the metallic electrodes are consumed whereby the pool of molten metal is maintained in contact with the lower ends of the metallic electrodes as the metallic electrodes are consumed.

According to another aspect of the invention, there is provided an apparatus suitable for producing tubular bodies, which apparatus comprises:

1. a mould which delimits an annular moulding space;

2. a support member for supporting a plurality of metallic electrodes so that their lower ends project into the annular moulding space;

3. control means to raise the mould at a controlled rate from a lower position to an upper position; and

4. means to supply an electric current to the metallic electrodes to melt the lower ends of the metallic electrodes; the arrangement of the apparatus being such that in operation the lower ends of the metallic electrodes are melted to form a pool of molten metal in the annular moulding space, from which pool the desired tubular body is formed, and the mould is raised as the lower ends of the metallic electrodes are consumed whereby the pool of molten metal is maintained in contact with the lower ends of the metallic electrodes as the lower ends of the metallic electrodes are consumed.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further illustrated by reference to the accompanying drawings showing, by way of example, an embodiment of the invention, in which:

FIG. 1 is a side elevational view of the apparatus, with portions shown in vertical cross-section; and

FIGS. 2 and 3 are sectional views taken along the line AA of FIG. 1 and respectively showing different arrangement of the metallic electrodes.

DETAILED DESCRIPTION OF THE DRAWINGS As shown in FIG. 1, a relatively shallow pit 2 is formed in a floor l. A base block 3 is provided on the floor of the pit 2 and substantially in the centre thereof. A ring gear 5 having an internal thread on its inner surface and gear teeth on its outer surface is rotatably mounted on the base block 3, by means of a bearing 4. Also situated in the pit 2 is a drive motor 7. A gear 6 is fixedly mounted on the end of the drive shaft of the drive motor 7 and is in meshing engagement with the gear teeth of the ring gear 5. Thus, the ring gear 5 is driven from the drive motor 7 in one or other direction about its own axis, while being held in its position. A spindle 8 having an external thread on its outer surface extends through the ring gear 5, with its external threads meshing with the internal threads of the ring gear 5. The top end of this spindle 8 is fixed to the centre of a bottom plate of an annular bracket 9a which projects above the floor 1 through an annular slit 1b formed in a floor plate la. A disc-like table 9 having a central bore 9b is fixed to the upper edge of the annular bracket 9a. The disc-lilte table is situated horizontally and the bore 912 is in axial alignment with the spindle 8. A start piece which is a short tube whose transverse sectional shape is the same as that of the tubular body to be produced is fixedly mounted on the table 9 and is concentric therewith. The apparatus is arranged so that, when a water-cooled metal mould M to be described later is at the lower end of its stroke, the top end of the start piece 10 is received in a central, parallel-walled portion of an annular moulding space in the metal mould, where its upper face closes the annular space at the boundary between the central parallelwalled portion of the annular space and an upwardly opening enlarged portion of the annular space. Since the start piece 10 is connected to the spindle 8 through the table 9 and annular bracket 9a, as described above, when the drive motor 7 is driven in one or the other direction, the start piece 10 is moved upwards or downwards in a vertical direction within the effective stroke of the spindle 8 while rotating in one or the other direction together with the spindle 8. in the pit 2 there is also provided a control box 1 1 which is electrically connected with the drive motor 7. The drive motor 7 is driven in one or the other direction at an optional speed by a signal given thereto from the control box 1 l. The control box 11 is connectedelectrically with a Geiger counter 27 which is a part of detecting means, to be described later, which is provided for detecting the surface level of a molten metal pool formed in the metal mould M. The control box 11 transmits a signal to the drive motor 7 according to the intensity of radiant ray sensed by the Geiger counter 27, to control the operation of the drive motor 7. The drive motor 7, the spindle 8, the table 9, the start piece 10 and the control box 11 all together constitute control means, to be described later, which always maintains the surface of the pool of molten metal in the metal mould at a predetermined constant level. An AC. power source 12 is provided on the floor 1 and is electrically connected to the table 9 and to a ring-shaped disc 16, to be described later, by wires a and b respectively which are arranged in such a manner that they will not interfere with rotation or vertical movement of the table 9 and disc 16. A ceiling plate 13 is provided squarely above the floor plate 1a and a vertical threaded spindle 30 extends between the centres of the ceiling plate 13 and floor plates la. The spindle 30 is in axial alignment with the spindle 8 and rotatably supported by the plates 13 and 1a by means of bearings 32 and 31. The top end of the spindle 30 extends upwards through the ceiling plate 13 and is connected to the drive shaft of a motor 33 which is mounted on a bracket 13a provided on the upper surface of the ceiling plate 13. The motor 33 is electrically connected to the aforesaid control box 11 and is driven at an optional speed or stopped by a signal supplied from the control box. The ring-shaped disc 16 has teeth formed on its outer peripheral surface and is rotatably supported by means of a bearing 15 on a bracket 14 which projects downwards from the lower surface of the ceiling plate 13. The disc 16 acts as a support member for supporting a plurality of metallic electrodes 19 in their pre-set positions respectively. It is provided on its lower surface with a plurality of equally spaced fixing means arranged around the circumference of a circle of a predetermined diameter, to which the top ends of the metallic electrodes 19 are fixed so that the electrodes are substantially vertical. Each metallic electrode 19 is of such a length that, when the water-cooled metal mould M, to be described later, is at the lower end of its stroke, the lower end of the metallic electrode is located at'about the centre of the enlarged upwardly opening portion of the annular moulding space in the metal mould. The arrangement of the metallic electrodes 19 in a horizontal plane is as shown in FIGS. 2 or 3.

Another motor 17 is mounted, by means of a bracket 13b, at a suitable location on the ceiling plate 13. A gear 18 is fixedly mounted on the drive shaft of the motor 17 and meshes with the teeth provided on the outer peripheral surface of the ring-shaped disc 16. The arrangement is such that when the motor 17 is set in motion the metallic electrodes periodically move bodily round the axis of the disc 16 at an optional speed and integrally with the disc 16 in one or other direction, without moving in a vertical direction. Each of the metallic electrodes 19 is electrically connected via a contact shoe 20 and the disc 16 to the aforesaid AC. power source 12 to be supplied with a current therefrom. The metal mould M consists of a water-cooled core mould 21 and a water-cooled outer mould 22. Both of the core and outer moulds 21, 22 are cooled by water circulating therethrough. Cooling water is supplied from a water tank not shown by a pump and a distributor, also not shown, and is introduced into each mould from an inlet port 23. After passing through the mould, the water is discharged from an outlet 24 to be returned to the water tank. The core mould 21 and outer mould 22 define therebetween an annular moulding space which, in a vertical cross-section, has an enlarged upwardly opening portion in the shape of a hopper, a cylindrical parallel-walled central portion and a downwardly expanding conical portion as shown in FIG. 1. The transverse cross-sectional shape of the central parallel-walled portion is the same as that of the tubular body to be produced. The core mould 21 is provided at a suitable location therein with a radiation emitter in the form of an isotope 26. This isotope 26 emits y-radiation in a horizontal direction from a position slightly lower than the boundary between the central parallel portion and the upwardly opening portion of the annular moulding space of the metal mould M. The 'y-rays emitted by the isotope 26 penetrate through the central parallel portion of the moulding space and enter a radiation detector, a Geiger counter 27 which is provided in the outer mould 22 at the same level as the isotope 26. Upon receiving the y-rays, the Geiger counter 27 generates a signal according to the intensity of the y-rays, which signal is transmitted to, and actuates, the control box 11. The isotope 26 and the Geiger counter 27 together constitute the detecting means for detecting the surface level of the pool of molten metal 45 to be described later. The annular core mould 21 has at the central portion thereof arms 28 each having a nut 29 fixed thereto, which nuts 29 are held in meshing engagement with the vertical threaded spindle 30. Thus, it will be understood that the core mould 21 moves upwards or downwards in a vertical direction at a predetermined speed, corresponding to the rate of rotation of the spindle 30. Elongate worms 38 and 38' extend upwards between the floor 1 and ceiling plate 13 and are rotatably supported by the floor and ceiling plates by means of bearings 39, 40 and 39, 40 respectively, as shown in FIG. 1. The top ends of these elongate worms 38 and 38' project upwards through the ceiling plate 13 and pulleys 35 and 35 are fixedly mounted on their projecting ends, respectively. Pulleys 34 and 34' are fixedly mounted on the upwardly projecting end of the spindle 30, and belts engage around the pulleys 34, 35 and 34, 35'. Thus, the elongate worms 38 and 38 are driven simultaneously by the motor 33, by means of these pulleys and belts, in one or the other direction, in the same direction of rotation and at the same speed as the spindle 30. The annular outer mould 22 is provided with support arms 36 and 36, respectively having nuts 37 and 37' fixed to the outer ends thereof, which nuts 37 and 37 are held in meshing engagement with the worms 38 and 38' respectively. Therefore, the outer mould 22 moves upwards or downwards corresponding to the rotation of the worms 38 and 38 in one or other direction in synchronism with the movement of the core mould 21. The upright threaded spindle 30, the elongate worms 38 and 38 and the motor 33 to drive the spindle and worms, together constitute elevating means for moving the metal mould M up or down in a vertical direction at a predetermined speed. Flux supplying hoppers 42 and 42' are respectively supported by support arms 42a and 42a, with their bottom openings located above the upwardly opening portion of the annular moulding space of the metal mould M. The support arms 42a and 42a respectively have nuts 41 and 41 threadably mounted on the worms 38 and 38'. These hoppers 42 and 42' also move upwards or downwards corresponding to the rotation of the worms 38 and 38 in one or the other direction, in synchronism with the movement of the metal mould M.

In producing a tubular body 25 using the apparatus described above and shown in the drawings, the motor 33 is first set in motion to bring the metal mould M to the lower end of its stroke. The top end of the start piece is received in the central parallel-walled portion of the annular moulding space in the metal mould M, whereby the annular moulding space is closed by the start piece at the boundary between the top opening portion and the central parallel-walled portion of the annular moulding space. Then, a plurality of metallic electrodes 19 are fixed to the lower surface of the ring-shaped disc 16 by suitable means in a positional relation as shown in FIGS. 2 or 3, in such a manner that the lower end of each metallic electrode 19 is located within the top opening of the annular moulding space of the metal mould M. Thereafter molten slag prepared previously by melting a flux is poured into the top opening of the metal mould M to form a slag pool 43, into which the lower end of each metallic electrode 19 dips. When the circuit of the AC. power source 12 is closed, a current flows through the electric wire a, the contact shoe 20, the disc 16, the metallic electrodes 19, the slag pool 43, the start piece 10 and the electric wire b, and electroslag re-melting of the metallic electrodes 19 takes place in the slag pool 43. Thus, each metallic I electrode 19 is melted from its lower end and the resultant droplets 44 of molten metal fall through the slag pool 43 and accumulate on the upper face of the start piece 10, forming a molten metal pool 45. The metal mould M is continuously raised by the motor 33 at a predetermined speed and consequently the start piece 10 slides downwards relative to the central parallelwalled portion of the annular moulding space, so that the molten metal accumulating continuously on the start piece 10 is drawn through the central parallelwalledportion of the annular moulding space. During this period, the molten metal is moulded into a tubular body having the same transverse cross-sectional shape as that of the central parallel-walled portion of the annular moulding space, and the inner and outer surfaces of the tubular body are cooled and solidified by the water-cooled core and outer moulds 21 and 22 of the metal mould M. Thus, the tubular body 25 is continuously formed. Due to the upward movement of the metal mould M, the lower end of each metallic electrode 19 is maintained in the slag pool 43 and is continuously melted. This continues until the metal mould M nears the upper end of its stroke, or in other words, until each of the metallic electrodes 19 is substantially completely melted by electroslag melting and the tubular body 25 having a length substantially equal to the initial length of the metallic electrodes 19 is formed on the start piece 10. Upon completion of moulding of the tubular body 25 in the manner described, the metal mould M is elevated to the upper end of its stroke to permit removal of the tubular body from the metal mould, following which the tubular body 25 is cut off the start piece 10 and removed from the apparatus by suitable conveying means, whereby one cycle of production of the tubular body 25 is completed.

In the tubular body production cycle described above, the slag forming the slag pool 43 flows downward through the slight gaps between the inner surface of the tubular body 25 and the core mould 21 and between the outer surface of said tubular body and the outer mould 22, and solidifies on the inner and outer surfaces of the tubular body, forming a thin slag film 46 thereon. These slag films 46 provide lubrication between the tubular body 25 and the core and outer moulds 21 and 22, and also prevent the molten metal from attaching to the core and outer moulds 21 and 22, thereby providing for smooth elevation of the metal mould M and increasing the available percentage of the material of which the tubular body 25 is made. The amount of slag thus consumed is made up by an equivalent amount of the granular flux supplied from the slag supplying hoppers 42, so that the volume of the slag pool 43 is always maintained constant.

The a-rays emitted from the isotope 26 which is provided in the core mould 21 pass at a level close to the boundary between the top opening portion and central parallel-walled portion of the annular moulding space of the metal mould M. When the surface level of the molten metal pool 45 fluctuates and rises above the level of the said boundary, the intensity of the radiation being received by the Geiger counter varies due to passage of the y-rays through the molten metal pool. The Geiger counter transmits to the control box 11 a signal which corresponds to the dosage variation, and thereby actuates the control box 1 1. Upon actuation of the control box 11, the motor 7 is driven in the normal direction to move the start piece 10 downward through the gears 6 and 5, the threaded spindle 8 and the table 9, and thereby to bring the surface level of the molten metal pool 45 back to the predetermined position. Conversely, when the surface level of the molten metal pool 45 drops excessively the intensity of radiation sensed by the Geiger counter through the molten slag 43 differs from that in the preceding case, so that the aforesaid respective members operate in the reverse manner, elevating the start piece 10 and thereby raising the surface level of the molten metal pool back to the predetermined position. In the manner described, the surface level of the molten metal pool 45 is always maintained in the predetermined position, providing for smooth formation of the tubular body 25..

The arrangement, in a horizontal plan view, of the metallic electrodes 19 may be as shown in either FIGS. 2 or 3, and smooth formation of the tubular body 25 is assisted particularly when the metallic electrodes are arranged substantially uniformly over the entire transverse cross-section of the tubular body as shown in FIG. 2. However, if the interval of the metallic electrodes 19 is too large as seen in the arrangement of FIG. 3, there may arise the problem that heat concentration occurs at a portion below each electrode or accumulation of the molten metal becomes non-uniform. This problem can be eliminated by periodically rotating or reciprocating the disc 16 at a suitable speed by means of the motor 17. This is indicated by the arrows 47 and 48 in FIG. 3. The respective metallic electrodes are rotated bodily together with the disc 16.

By means of the invention as described and illustrated above there can be achieved the following practical advantages:

1. Since the electroslag re-melting of the metallic electrodes is carried out by continuously raising the metal mould at a controlled speed, the metallic electrodes are maintained stationary in their pre-set positions, the height required to accommodate the apparatus can be reduced to as low as about the length of the metallic electrodes 19 plus the height of the start piece 10 and other accessories. Therefore, the height of the apparatus according to the invention is substantially lower than that of the apparatus used previously in J apan. This is advantageous in eliminating, not only the considerable construction work which has heretofore been necessary for increasing the height of a building in which the apparatus is to be installed or for constructing a deep pit for reducing the height of the building, but also provision of a tall jack means.

2. The construction cost of the apparatus can be reduced because such facilities as metallic electrode feeding means and product drawing means are not required.

3. Since the metal is being continuously raised as the molten metal accumulates in the central parallel portion of the annular moulding space, the molten metal fills the portion of the annular moulding space more compactly and hence the slag film 46 formed is thinner than in the case of the apparatus previously known in Japan, in which a tubular body is drawn by drawing means. Therefore, a higher quality product can be obtained with smoother inner and outer surfaces than by the conventional apparatus.

4. Since the surface level of the pool 45 of molten metal is always maintained at a predetermined position, by detecting means consisting of the isotope 26 and Geiger counter 27, and control means operated by a signal from the detecting means, a tubular body 25 can be obtained smoothly and with high quality.

It is also to be noted that according to the invention, as described previously, the metallic electrodes 19 are bodily rotated with the disc 16 rotated by the motor 17, so that the temperature throughout the slag pool 43 is maintained uniform as a result of said slag pool being 6 stirred by the electrodes. Furthermore, the droplets 44 formed by continuous melting of the electrodes are distributed uniformly in the molten metal pool 45. This brings about the advantage that the quality of the product can be further enhanced.

We claim: 1. Apparatus suitable for producing tubular bodies comprising:

a. a mould which delimits an annular moulding space;

b. a support member for supporting a plurality of metallic electrodes so that their lower ends project 10 into the annular moulding space;

0. control means to raise the mould at a controlled rate from a lower position to an upper position; and

5 d. means to supply an electric current to the metallic l electrodes to melt the lower ends of the metallic electrodes; the arrangement of the apparatus being such that in operation the lower ends of the metallic electrodes are melted to form a pool of molten metal in the annular moulding space, from which pool the desired tubular body is formed, and the mould is raised as the lower ends of the metallic electrodes are consumed whereby the pool of molten metal is maintained in contact with 2 the lower ends of the metallic electrodes as the lower ends of the metallic electrodes are consumed; the apparatus further comprising:

e. a table for supporting a start piece which projects into the annular moulding space from below when the mould is in the lower position;

f. means for raising and lowering the table to raise or lower the start piece and assist in maintaining a constant surface level of the pool of molten metal.

2. Apparatus as claimed in claim 1 in which the mould comprises a core mould and an outer mould which define the annular moulding space between them and are adapted to be water-cooled.

3. Apparatus as claimed in claim 1 which comprises means to observe the surface level of the pool of molten metal in the annular moulding space and to actuate the control means to raise the mould at a rate which maintains the surface level of the pool of molten metal in the annular moulding space constant.

4. Apparatus as claimed in claim 1 in which the said observing means comprise a radiation emitter and a radiation detector, one mounted on the core mould and one mounted on the outer mould.

5. Apparatus as claimed in claim 1 which comprises means for moving the said support member to move the lower ends of the metallic electrodes around the annular moulding space to create an even heat distribution in the pool of molten metal.

6. Apparatus as claimed in claim 1 which comprises hoppers for supplying flux to the annular moulding space, which and means for raising the hoppers with the mould.

7. A method of producing a tubular body, comprismg:

continuously melting the lower ends of a plurality of metallic electrodes by electroslag melting to form a pool of molten metal in a mould configured to form a desired tubular body from the molten metal, upon a start piece disposed beneath the mould; continuously raising the mould as the metallic electrodes are consumed, at a raising rate which keeps the lower ends of the metallic electrodes in contact said level. v 8. The method of claim 7 wherein said pool is annular and the plurality of electrodes is arranged in a circular array and is moved circularly around the pool to more uniformly distribute heat in said pool. 

1. Apparatus suitable for producing tubular bodies comprising: a. a mould which delimits an annular moulding space; b. a support member for supporting a plurality of metallic electrodes so that their lower ends project into the annular moulding space; c. control means to raise the mould at a controlled rate from a lower position to an upper position; and d. means to supply an electric current to the metallic electrodes to melt the lower ends of the metallic electrodes; the arrangement of the apparatus being such that in operation the lower ends of the metallic electrodes are melted to form a pool of molten metal in the annular moulding space, from which pool the desired tubular body is formed, and the mould is raised as the lower ends of the metallic electrodes are consumed whereby the pool of molten metal is maintained in contact with the lower ends of the metallic electrodes as the lower ends of the metallic electrodes are consumed; the apparatus further comprising: e. a table for supporting a start piece which projects into the annular moulding space from below when the mould is in the lower position; f. means for raising and lowering the table to raise or lower the start piece and assist in maintaining a constant surface level of the pool of molten metal.
 2. Apparatus as claimed in claim 1 in which the mould comprises a core mould and an outer mould which define the annular moulding space between them and are adapted to be water-cooled.
 3. Apparatus as claimed in claim 1 which comprises means to observe the surface level of the pool of molten metal in the annular moulding space and to actuate the control means to raise the mould at a rate which maintains the surface level of the pool of molten metal in the annular moulding space constant.
 4. Apparatus as claimed in claim 1 in which the said observing means comprise a radiation emitter and a radiation detector, one mounted on the core mould and one mounted on the outer mould.
 5. Apparatus as claimed in claim 1 which comprises means for moving the said support member to move the lower ends of the metallic electrodes around the annular moulding space to create an even heat distribution in the pool of molten metal.
 6. Apparatus as claimed in claim 1 which cOmprises hoppers for supplying flux to the annular moulding space, which and means for raising the hoppers with the mould.
 7. A method of producing a tubular body, comprising: continuously melting the lower ends of a plurality of metallic electrodes by electroslag melting to form a pool of molten metal in a mould configured to form a desired tubular body from the molten metal, upon a start piece disposed beneath the mould; continuously raising the mould as the metallic electrodes are consumed, at a raising rate which keeps the lower ends of the metallic electrodes in contact with the molten metal and the level of molten metal substantially constant in the mould; observing the tendency of said level of molten metal to vary, and varying the disposition of the start piece in a vertical sense in response to said observation, to assist in maintaining the constancy of said level.
 8. The method of claim 7 wherein said pool is annular and the plurality of electrodes is arranged in a circular array and is moved circularly around the pool to more uniformly distribute heat in said pool. 